Metallurgical stirrer construction

ABSTRACT

A stirrer for metallurgical purposes particularly for the treatment of pig iron, steel or cast iron melts during desulfurization desilication, carbonization or addition of other metallurgical reactants, includes a rotatable tubular element or body preferably having at least two radially extending delivery conduits which communicate centrally with a central suction passage. The body is provided on its inside with a reinforcement and on its outside with a heat resistant material and advantageously includes axial and transverse intersecting tubular elements formed of high silicon steel alloyed with aluminum and chromium and having a coating of synthetic slag.

Inventor Hubert Polomsky Duisburg-Buchholz, Germany Appl. No. 817,057

Filed Apr. 17, 1969 Patented 0ct.'5, 1971 Assignee DemagAktiengesellschaft Duisburg, Germany Priority Apr. 20, 1968 Germany P 1758 194.1

METALLURGICAL STIRRER CONSTRUCTION 8 Claims, 3 Drawing Figs.

416/224, 416/241 Int. Cl B011 9/12 Field of Search 416/91,

[56] References Cited UNITED STATES PATENTS 3,326,534 6/1967 Pryde416/241 X FOREIGN PATENTS 85,394 7/1958 Denmark 416/91 29,737 11/1958Finland I 416/91 143,372 11/1963 U.S.S.R. 416/241 PrimaryExaminer-Everette A. PowellJr. Attorney-McGIew and Toren ABSTRACT: Astirrer for metallurgical purposes particularly for the treatment of pigiron, steel or cast iron melts during desulfurization desilication,carbonization or addition of other metallurgical reactants, includes arotatable tubular element or body preferably having at least tworadially extending delivery conduits which communicate centrally with acentral suction passage. The body is provided on its inside with areinforcement and on its outside with a heat resistant material andadvantageously includes axial and transverse intersecting tubularelements formed of high silicon steel alloyed with aluminum and chromiumand having a coating of synthetic slag.

PATENTED UB1 5 I97! SHEET 1 [IF 2 Inventor hIJEPT p 1,, x,

PATENTED OCT 5 97 SHEET 2 [IF 2 Inventor H0850) Relay METALLURGICALSTIRRER CONSTRUCTION SUMMARY OF THE INVENTION This invention relates, ingeneral, to metallurgical devices and, in particular, to' a new anduseful stirrer for metallurgical purposes particularly for the treatmentof pig iron, steel or cast iron melts during desulphurization,desilication, carbonization or addition of reactants and which isprovided with a reinforcement on its inside and an outside coating of aheat resistant material.

It is known to design metallurgical stirrers as beam stirrers having afull cross section or to provide a pumplike body which consists of atubular part for the suction and one or more tubular parts radiallyarranged for outward centrifugal discharge. in all cases, the moldedpart of refractory material is provided with a steel reinforcement whichis rigidly connected with the drive shaft and thus capable oftransmitting the torque. The inner reinforcement can also be air cooledby using tubes as reinforcing rods so that no critical influences can beformed which will influence the strength of the device.

A stirrer which is formed of refractory material is exposed to thedirect heat of a molten bath of up to l,500 C. and even more, and it isalso subject to additional greater stresses. According to theliterature, for example, Journal Giesserei of Mar. 28, 1968, only themanufacturing method and the durability of the stirrers are thedeterminant factors for the profitability of such stirring methods.Giesserei mentions that it has been found in practice that one of themost important factors of wear is the stress under sudden changes oftemperature (Giesserei 1966 No. 23, pages 816 and 818). The stirrer isdipped without preheating directly into the liquid iron and broughtagainst the ambient air after use without any special precautions andsuch a rough treatment leads to small cracks in the surface of theceramic material.

Though the danger of cracking could be reduced by suitable measures, forreducing stress under sudden changes in temperatures, otherinconveniences could not be eliminated. The properties of the ceramicmaterial and the substances of the reaction carriers are such that theyproduce deposits on the stirrer during the metallurgical process andeven to a greater extent during the cooling of the stirrer. Thisincreases not only the weight of the stirrer, but also its capacity forforming a desired flow. Cleaning the ceramic body shortly after stirringcannot be carried out by the operators because of the great heat, and,only after the stirrer is cooled, is it possible to remove the slagwhich adheres thereto and becomes hard enough to require this use ofspecial removing tools. The mechanical removal of the melt and slagresidues is costly and risky. There is a great danger that the stirrerwill be damaged, that is, that parts of its circumference will beremoved. Stirrers encrusted with slag cannot be kept completely hotapart from the fact that a considerable amount of heat must beconsidered as lost.

The known stirrers do not meet the requirements of modern manufacturingmethods and their construction is not satisfactory. The ceramic materialwhich is used to form a stirrer requires a mold and any reinforcementsfor the material must be inserted with accuracy in order to form a corewhich permits the body of the ceramic material to be applied in theliquid or pasty form around the core. In the solidified state, the bodyreaches the final state after a prolonged burning process. Such amanufacturing method requires very large apparatus even for simplestirrers and they are not available for every metallurgical plant. Forhollow stirrers, which yield special results, the expenditures increasebecause of the special cores which are required. Charge durabilityvalues which have already been obtained and the results of the degree ofpurity achieved show that it may be advisable to use more complicatedstirrers in order to achieve better metallurgical results. Thus, forexample, it is preferable that the stirrer be capable of circulating theentire melt of the reactive slag composition in the shortest period oftime and not merely to mix this composition. lt was found that this wasfar more economical because the durability of the lining materialincreases with low slag costs and good circulation of the molten bath.The lining of the reaction vessel is destroyed very rapidly with asimplestirring tool and with highly aggressive slags and they are alsomore expensive.

in accordance with the present invention, there is provided a stirrer ofsimple construction which is better for the particular metallurgicaloperative use than the known stirrers and which is durable and capableof long operation. The invention provides a metal body forming thecontour of the stirrer which is bonded together with a heat resistantcoating. With such a construction, the resistance to mechanicaltreatment of the stirrer structure is great so that slag residues orsimilar deposits can be removed, for example, by chilling the body in amedium of much lower temperature. Mechanical treatment can also becompletely avoided by cooling the stirrer from its operating temperatureof over l,000 C. in a water bath or an air current of very much lowertemperature so that the abrupt cooling will cause the slag to break off.In the preferred form, the stirrer is made up of a plurality of tubularbodies, for example, a central tubular body comprising the suctionportion and one or more radially extending tubular bodies which arejoined to the central portion such as by welding. A heat-resistantcoating is then produced over the body, for example, by dipping thebody. The coating which is formed may be either detachable orundetachable, and, in the case of an undetachable coating, aparticularly thin layer is used. If the coating is to be removed later,it can be formed as a simple ring which may be inserted or attachedaround the stirrer body.

A particular advantage of the construction is that, even if the outercoating deteriorates or wears off, the interior body may be recoated.

In accordance with one embodiment of the invention, a stirrer isprovided which is suitable for stresses which are produced by suddentemperature changes and caused by frequent cooling and reheating. Inthis case, the body cornprises a high silicon steel alloyed withaluminum and chromium and the coating comprises a synthetic slag. Theinventive construction utilizes the characteristic of the higher meltingpoint of the synthetic slag with respect to the lower temperature of theoperation of steel baths.

in accordance with another feature of the invention, the stirrerconstruction is formed of a plurality of tubular elements which areprovided both on the inside with liners of ceramic material which areremovable. With such a construction, the liners may be readily replacedafter long operating periods, if necessary. Thus, both the manufactureand the replacement of such stirrers are greatly facilitated. It shouldbe appreciated that during operation as well as under continuousalternating stresses, within very wide temperature ranges, the stirrercan perform its function only when there is a good bond between the bodyand the coating. In addition, the mechanical removal of the slagprovides a further stressing of the bond between these parts. It istherefore desirable that the surfaces of the body are made uneven inorder to provide a greater anchoring of the coating. The stirrer isadvantageously made of a plurality of individual parts which may befitted together and the ceramic inserts may be inserted into the partsafter they are fitted together or the parts may be dipped in a coatingbath to apply a light coating thereto.

When metallurgical deposits form on the stirrer during operation, theynot only increase the weight of the stirrer and make the powerrequirements for rotating the stirrer higher, they also present adisadvantage because they must be kept hot when the stirrer is removedfrom the melt. The inventive construction permits the easy detachment ofthe adhering residues and enhances the flow conditions accordingly. Tothis end, the inner and/or outer parts of the body are made conical inthe form of a diffuser. An inner conicity enhances the detachment of themetallurgical slag regardless of whether it is accomplished bymechanical means or by shrinkage. Such a design of the flow ducts,however, provides a considerable influence on the velocity and pressureconditions.

In metallurgical processes, it can be expected that molten metals of anytype will carry slag parts which will float on the melt or be suspendedinside the bath depending of the phase of the stirring process. Whenhollow stirrers are employed, the slag pieces can produce clogging ofthe stirrer. It is also possible that such semisolid melt parts of slagwill be pressed into the interior when the stirrer is dipped into themolten bath which is covered with the solid reactants. In order to avoidsuch difficulties, the inventive construction provides a stirrer withteeth which operate during the rotation of the stirrer to crush the slagparts. Particularly for a hollow stirrer, it is preferable according tothe invention, that the inlet of the suction pipe be provided with ductswhich are opened at the bottom and which widen in a radial orcircumferential direction. The portion on each side of the ducts formteeth and the arrangement of the slots or ducts therebetween produces awhirling of the melt and the forcing of the melt to the outside withoutgetting immediately into the circulation proper at the time that it isintroduced. As a rule, only liquid material will therefore rise in thestirrer itself so that deposits which could have been formed byseparation from the melt will have no opportunity to deposit on thewalls of the stirrer.

Accordingly, it is an object of the invention to provide an improvedstirrer construction which includes a body made of a rigid material suchas ametal and having a coating of a slag material.

A further object of the invention is to provide a rotatable stirrerwhich comprises a plurality of tubular portions including a central oraxially extending tubular portion forming a suction tube and one or moreradially extending tubular portions forming centrifugal discharges andwherein a coating of a slag material is applied over the body either inthe form of a coating or a separate jacket and also wherein the passagesformed in the tubular elements are advantageously made conical and theinlet to the passages, particularly the suction inlet, is provided withteeth elements defining inflow passages therebetween.

A further object of the invention is to provide a stirrer which issimple in design, rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference should be had to the accompanying drawings and descriptivematter in which there are illustrated preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings FIG. 1 is a sectionalview of a stirrer constructed in accordance with the invention;

FIG. 2 is a partial perspective view of the suction end of a stirrer ofanother embodiment of the invention; and

FIG. 3 is a view similar to FIG. 1 of another embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to thedrawings, in particular, the invention embodied therein in FIG. Icomprises a stirrer generally designated 50 which includes a metallicbody or core 1 having a corrugated or wavy exterior and interior surface2. A coating 3 of a synthetic slag material is applied over both theinterior and exterior surfaces, for example, by dipping and thecorrugations ensure that the coating is retained. In the embodiment ofFIG. I, the stirrer 50 includes a vertical suction pipe portion 4 andlaterally and radially arranged ejection pipes or discharge pipes 5 and6 which, in the embodiment shown,extend-outwardly in respectiveoppositedirections. The body 1 is in form locking and force-locking connectionto a drive shaft 7 which is rotated by means (not shown).

The suction tube 4 includes an inlet or suction 8 which may be of theconfiguration indicated in FIG. 1, or may be provided with a pluralityof circumferentially spaced teeth 9 as indicated by the suction 8' inFIG. 2. The teeth 9 are formed as axial or radial projections. The gapsbetween the teeth 9 form ducts 10 which are formed to the generalconfiguration of a centrifugal pump impeller in order to effect anacceleration of the material radially to the outside.

In FIG. 2, the ducts 10 have a curved configuration, but they can bemade with simple straight walls, if desired. The ducts 10 areadvantageously worked into the body portion comparable to the body 1 ofFIG. 1 so that the subsequent methods for coating with synthetic slag orsimilar heat resistant coating materials will enclose only the preshapedbody form.

In accordance with the embodiment of the stirrer 50, indicated in FIG.3, there is provided a body generally designated 1 made of a metal orsimilar material which is formed of a plurality of separate conicaltubes or pipes including suction tube 4' and discharge or ejection tubes5' and 6'. A conical interior configuration 16 helps to permit theentrance of a large amount of metal material during operation. The flowis accelerated to the interior of the stirrer through the suction duct4' and accelerated and transformed into pressure energy as it issuesfrom the ejection tubes 5 and 6'. This produces a particularly intensivecontact of the bath particles with the slag materials. It also providesmeans for breaking of the slag at the inlet and at the outlet ports ofthe suction tube 4' and the outlet tubes 5' and 6' in the cold state ofthe stirrer.

In the embodiment of FIG. 3, the body portion 1' includes an uppertubular part 15 which is secured to a shaft 7' for rotation therewithand this is assembled to the ejection tubes 5' and 6, such as by weldingor bolting together at the conical surfaces 13 and 14 of these tubes tothe suction tube 4. The assembled boy 1' is then provided with a coating3 of a heat resistant material which is effected by dipping it into abath, for example, of a material such as a synthetic slag.

I claim:

1. A stirrer for metallurgical purposes particularly for treatment ofpig iron, steel or cast iron melts during desulphurization,desilication, carbonization or addition of other reactants, comprising arigid tubular stirrer body which is adapted to be rotated and includingat least one transversely extending portion inclined upwardly towardeach end from its center and an axial tubular portion extendingdownwardly from the center of said transversely extending portion andhaving an interior communicating with the interior of said transverselyextending portion, and being of a length longer than the length of thetransversely extending portion which extends from its center to eitherend thereof, and a reinforcement coating on the inside and outside ofsaid body of a heat resistant synthetic slag material, said tubularstirrer body being made of a high silicone steel alloy with aluminum andchromium.

2. A stirrer according to claim 1, wherein said body is covered on theinside and outside with rings of ceramic coating material.

3. A stirrer according to claim 1, wherein said axial tubular portioncomprises a separate conical portion forming a suction passagecommunicating at the center with transversely extending portion.

4. A stirrer for metallurgical purposes, particularly for the treatmentof pig iron, steel or cast iron melts during desulphurizationdesilication, carbonization or addition of other reactants, comprising arigid tubular stirrer body which is adapted to be rotated, and areinforcement coating on the inside and outside of said body of aheat-resistant material, said body being formed with corrugations on theexterior and interior surface thereof to facilitate adherence of thecoating thereto.

5.. A stirrer, according to claim I, wherein said coating comprisesseveral layers.

' 6. A stirrer, according to claim 1, wherein said coating comprisesaceramic insert located within said tubular portion.

7. A stirrer, according to claim 1, wherein said body portion includes asuction portion of conical configuration and at least one transversedischarge portion of conical configuration.

8. A stirrer, according to claim 1, wherein said and tubular

2. A stirrer according to claim 1, wherein said body is covered on theinside and outside with rings of ceramic coating material.
 3. A stirreraccording to claim 1, wherein said axial tubular portion comprises aseparate conical portion forming a suction passage communicating at thecenter with transversely extending portion.
 4. A stirrer formetallurgical purposes, particularly for the treatment of pig iron,steel or cast iron melts during desulphurization desilication,carbonization or addition of other reactants, comprising a rigid tubularstirrer body which is adapted to be rotated, and a reinforcement coatingon the inside and outside of said body of a heat-resistant material,said body being formed with corrugations on the exterior and interiorsurface thereof to facilitate adherence of the coating thereto.
 5. Astirrer, according to claim 1, wherein said coating comprises severallayers.
 6. A stirrer, according to claim 1, wherein said coatingcomprises a ceramic insert located within said tubular portion.
 7. Astirrer, according to claim 1, wherein said body portion includes asuction portion of conical configuration and at least one transversedischarge portion of conical configuration.
 8. A stirrer, according toclaim 1, wherein said and tubular portion is arranged along the axis ofrotation and forms a suction conduit, said axial tubular portion havingan inlet formed by a plurality of circumferentially spaced teethdefining inlet passages therebetween.